Process of separating meta- and para-cresols.



FRANZ ELGER. 0F BASEL, SWITZERLAND, ASSIGNOR TO HOFFMANN-LA ROCHE CHEMICAL WORKS, OF NEW YORK,

N. Y. A CORPORATION OF NEW YORK.

PROCESS OF SEPAR-ATING META- AND PA RA-CRESOLS.

No Drawing.

To (Z Z70/1 7721flhtdf/COWOCTH.

Be it known that I. Fnaxz ELGER. a subject of the Austro-l'lungarian Empire. and a resident: of Basel. Switzerland, have in vented certain new and useful Improveacids we find just the opposite effect. Metacresol-mrmosulioacid is not readily soluble in dilute sulfuric acid while the paracresolmonosulfo-acid is more readily soluble. This discovery lies at the root of the present invention. In the development of this discovery it became necessary to ascertain and devise the conditions necessary to obtaina reaction which leads to the formation of the cresol-n'ionosulfo-acids to the practical exclusion of the clisulfo-acid. In this connection a further observation was made. to wit: That the incta-t1-rcs l is more readily sulfonated than the para-cresol. This observation or discovery fixed as one of the fundamental fa ts that the sulfonation should be carried on with a limitedfamount of sulfuric acid so that practically only the monosulfoacids should be created. Inasmuch as the 'paivr-ta'escl is sulfonated with more ditliculty han the meta. the work of sulfonation was carried on with a less quantity of sulfonatine' material than would be theoretically reouired for the formation of the two nionosulfa-acids. The result ofthis practice is that a portion of the paraci'esol, remains unsull'onattd. and that portion may thereafter be withdrawn from the mixed solution of the react? i by means of a suital'ile solvent.

lflvcn if :--utlicient acid is used to;

Specification of Letters Patent.

Application filed October 19, 1911. Serial No. 655,562.

Patented May 7,1912.

to be converted into monosulfoacid. there would have to be used an excess of the sulfonating material over that which theoretically necessary to satisfy both crcscls. If, however. an excess of concentrated or fuming sulfuric acid is present, the chemical process is likely to continue so that at a time when there is still some free para-cresol in the mixture, a second sulfo-group is already entering into the meta-cresol-Inonosulfo-acid. It is obvious that the temperature used during the sulfonating process becomes very material in reactions of this character. lVith respect to this temperature, excellent results have been obtained with the use of a temperature of C. The action proceeds also, as has been ascertained,

at temperatures approximating 70 and even 100 C. But in these latter cases it has been found that certain small proportions of disulfo-acids have been found as a by-product. The work may also be carried on at a temperature lower than 35, but in that case the time of the react-ion will be increased.

From the above outline it will be observed that the essence of this invent-ion resides in the maintenance of conditions favorable to the formation primarily of the monosulfonic acids, and that formation of disulfonic acid is to be so far as possible avoided,

and that these results are accomplished by limiting the amount of the sulfonating reagent and also by causing the action to proceed at relatively low temperatures. As soon as a material excess of sulfuric acid or similar sulfonating reagent is employed,

: or as soon as a materially higher temperathe u'etienlly ctuivcrt the two crcsols intof nioiwsult'o-achls. there will still remain a portion of the puraa'rcsol not acted upon as the result of the. resistance of this body again t sulfonaticn. it therefore the two nonieric cresols in the mixture of cresols are ture than 100 C. is used, the tendency of the mixture will be to produce disulfo-acids and to result in the mixture of four acids, 1'. e. the two 1nonosulfo-acids and the two disulfo-acids of the respective cresols, and from such a mixture of four acids it is from a practical standpoint impossible to ettect a separation of relatively pure separated products.

In certain prior processes looking toward the separation of the metaand para-cresols the mixture of such cresols isheated with at least an equal Weight of funnngsulfor r acid. or one and a half times its weight of concentrated sulfuric acid at a relatively high temperature. The para-sulfonlc acid then crystallizes out of the reaction mixture.

In. that. case the separation of the cresols is effected by converting them into disulfonio acids, as is shown by the excess of sulfuric acid, the temperature of the reaction and the crystallization of the para-cresol-acid,which is in direct contrast with the process herein described, in which the meta-cresol crystallizes out, being first formed under conditions involving relatively low temperature and a limited amount of acid.

Another process has been suggested for effecting the separation between the two cresols, but I am not aware that this second process has ever been commercially employed. It deals with solids and not'with solutions and suggests the treatment of a mixture of the two cresols for from 8 to 10 hours at- 100-110 C. with four times the quantity by weight of sodium bisulfate containing pyrosulfate, if so desired. According to that treatment it is said that only the meta-cresol. is sulfonated, while the paracresol remains unchanged and can be separated from the meta-cresol sulfonate of sodium.

My process involves the separation of the meta-cresol sulfonic acid out of a liquid solution of the sulfonation mixture, thereby dis tinguishing from the two previously suggested processes, according to which either the para-acid crystallizes out first or a sodium sulfonate is separated as the result of separation of solid bodies. To carry out my process, the mixture is treated, at practically ordinary temperature or slightly warmed, with concentrated sulfuric acid and preferably with less acid than is theoretically necessary for the formation of the two sulfonic acids. As above explained, the'quantity of sulfuric acid may be increased to approximate the amount theoretically necessary to sulfonate both cresols, but in practice the success of the process when carried on with a limited amount of sulfuric acid and the expense of the sulfonating reagent makes the use of a' quantity of sulfuric acid restricted to less than that theoretically required to satisfy both cresols advisable and economical. Under these conditions of restricted quantities of sulfuric acid it is chiefly the metacresol which reacts, only a small portion of the para-cresol being attacked. This metacresol-sulfonic acid crystallizes out of the sulfonation mixture directly or in some cases even better after dilution with water or dllute sulfuric acid. In order to obtain the para-cresol, the remainder of the reaction llquid may be subjected to extraction with an organic solvent such as benzene (benzol). The separation of the meta-cresol-acid crystals may take place either before or after the extraction of the para-cresol, and thecresol mixture may be treated with the benzol solvent even before the sulfonating reactlon begins. In this latter. case the unsulfonated portion of the mixtureconsisting mainly of para-cresol-remains in the solvent and may be separated therefrom; but a certain portion of the para-cresol will undoubtedly during the sulfonating process reach the acid and be there dissolved or emulsionized. In such cases, therefore, in order to extract the complete quantity of unsulfonated cresol, a second extraction would be necessary after the first separation of the solvent. My preferred method of directing this portion of the process is to effect the extraction of the unsulfonated portion immediately after the completion of the sulfonation, because in that case the metacresol-monosulfo-acid as it crystallizes out cannot carry with it any unsulfonated product. The extraction may, however, nevertheless be effected after the meta-acid has crystallized out. The selection of either of these alternative processes will depend upon the specific object which the manufacturer has in view. It has already been shown that if the quantity of sulfuric acid or fuming sulfuric acid theoretically necessary for both cresols be used, a portion of para-cresol will nevertheless remain unsulfonated. In that case the meta-cresol sulfonic acid crystallizes out of the mixture of metaand paracresol sulfonic acid, while the para-cresol sulfonic acid remains behind in the mother liquor. The cresols may be recovered from the cresol sulfonic acids by any suitable method such for example as by distillation with superheated steam. As already stated, temperatures above 100 C. are to be avoided, as they tend to destroy the results aimed at by this invention. The use of these lower temperatures make the employment of positively applied heat almost entirely unnecessary, since the process proceeds favorably at a relatively very .low sulfonating temperature. This is a great advantage from the standpoint ofmanufacture. The separation of a solid meta-cresol-sulfo-acid is also an advantageous desideratum from the standpoint that the cresols in this condition can be directly used for the creation of derivatives of the meta-cresols. For the purpose of further clarifying the invention two concrete examples are submitted to show various methods of treatment employed:

Example 1: 1000 kg. of a mixture of metaand para-cresol, (containing about 60 per cent of metaand 40 per cent. of paracresol), are sulfonated with 750 kg. of fuming sulfuric acid, (containing 20 per cent. of S0,? at a temperature below 100 C., the mix me being well stirred. After the sulfonation is ended, the reaction mixture is mixed with 500 kg. of 50 per cent. sulfuric acid, the unsulfonated cresol extracted from the reaction product with benzene at a temperature of about 50 (3., and the solution then allowed to slowly cool down. The

meta-cresol may be obtained from the metacresol sulfonic acid, which has crystallized out, by treatment with super-heated steam, while the benzene extract, after distilling off the solvent, yields a para-cresol, which solidifies in the cold. j

Example 2: 1000 kg. of the mixture of metaand para-cresol are dissolved in 500 kg. of benzene, and 950 kg. of 96 per cent. sulfuric acid are allowed to flow in, the m'ixture being vigorously stirredat a temperature of about 40 C. After the sulfonation is ended, the mixture is diluted with water or dilute sulfuric acid, while being stirred, the benzene, which contains a portion of the para-cresol in solution, is separated, and the;

sulfonation mixture allowed to become cold. The meta-cresol-sulfonic acid crystallizes out in this case also, while the mother liquor yields on separation a mixture of cresols, in which the para-cresol is enriched in comparison with the starting material.

From these exam les it will be seen that I employ strong sul uric acid; in one. case fuming sulfuric acid and in the other, concentrated sulfuric acid, both of them in quantities approximating that necessary to satisfy the mono-sulfonization of the two cre-.

sols. When, therefore, in the claims I speak of strong sulfuric acid, I intend to refer generically to either the concentrated or the fuming sulfuric acid.

In the above two examples, I have described the process as employed in connection with a cresol mixture containing about 60% meta and.4:0% para; the process may,

however, be applied to mixtures having different percentages, and may even be repeated in connection with the product obtained as the result of each of the examples mentioned; and I desire my claims to be understood to cover the process as applied'either to the crude starting material, or -to the product, i. 6. commercial meta-cresol obtained as the final product of'each of the two examples, or in fact, to any cresol body which contains material proportions of, or is rich in the meta-cresol variety.

I claim:

1. That improvement in the process of separating meta and para-cresols which comprises the crystallizing of that component which retains the meta-cresol out of a liquid mixture containing the products resulting from the treatment of the two cresols with sulfuric acid.

2. That improvement in the process of separating meta and para-cresols which comprises treating a liquid mixture thereof with alimited quantity of sulfuric acid to convert the meta-cresol therein into a monosulfo acid under conditions unfavorable to the formation of any material quantity of its di-sulfo acid, and crystallizingthe metacresol-monosulfo acid out of the liquid mixture in the form of a solid crystalline compound.

3. That improvement in the process of separating 'metaand para-cresols which comprises in adding to a mixture thereof a limited quantity of strong sulfuric acid, the quantity of such acid approximating that which is theoretically necessary for the conversion of both cresols into their respective moncsulfonic acids. I

4. That improvement in the process of separating metaand para-cresols which comprises in adding to a mixture thereof a limited quantity of strong sulfuric acid, the quantity of such acid being less than that which is theoretically necessary for the conversion of both cresols into their respective monosulfonic acids.

5. The process of separating meta? and para-cresols which comprises treating a mixture thereof with a limited quantity of strong sulfuric acid until sulfonation is ended," the quantity of such acid approximating that which is theoretically necessary for the-conversion of both cresols into their respective monosulfonic acids, causing the formation of crystals in said sulfonated mixture, separating the solid and liquid portions of the mixture from each other and treatingv them respectively for the recovery'of their cresols.

6. The process of separating metaand para-cresols which comprises treating at a temperature materially below 100 C. a mixture thereof with a limited quantity of strong sulfuric acid until sulfonation is ended, the quantity of such acid approximating that which is theoretically necessary for the conversion of both cresols into their respective monosulfonic acids, causing the formation of crystals in said sulfonated mixture, separating the solid and liquid portions of the mixture from each other and treating them respectively for the recovery of their cresols;

7.- The process of separating metaand para-cresols which comprises treating a mixture thereof with'a limited quantity of strong sulfuric acid until sulfonation 1s ended and simultaneously stirring the m1xture, the quantity of such acid approximating that which is theoretically necessary for for the conversion of both cresols into their respective mono-sulfonic acids, causing the formation of crystals in said sulfonated mixture, separating the solid and liquid portions of the mixture from each other and treating them respectively for the recovery of their cresols.

8. The process of separating metaand para-cresols from a mixture thereof Wl'llCll comprises preparing a body of llquid containing unsulfonatedcresols capable of extraction by a suitable solvent, a readily ,crystallizable proportion composed mainly of meta-cresol-monosulfo-acid and a material proportion of paracresol-sulfo-acid. said mixture being prepared by means of treating the cresol mixture with a limited amount of strong sulfuric acid approximating that theoretically necessary for the formation of that of the monosulto acids of both cresols, separating said liquid mixture into its said three components and treating the acid components respectively for the recovery of their respective cresols.

9. The process of separating metaand para-cresols from a mixture thereof which comprises sulfonating the cresol mixture with a quantity of strong sulfuric acid approximating that theoretically necessary for the formation of the monosult'o acids of both cresols and separating from the resultant mixture metacresol-monosulto-acid in the form of crystals and unsulfonated cresols by a suitable solvent, leaving the major portion of the paracresol sulfonic acid in liquid form as the residuum and treating the acid components respectively for the recovery of their respective cresols.

10. The process of separating metaand para-cresol from a mixture thereof which consists in sulfonating the cresol mixture at a temperature below 100 C. while stirring the mixture, with a quantity of strong sulfuric acid approximating that theoretically necessary for the formation of the monosulfo acids of both cresols and separating from the resultant mixture metacresol monosulfo-acid in the form of crystals and unsulfonated eresols by a suitable solvent, leaving the major portion of the para-cresol sultonic acid in liquid form as the residuum and recoveringthe cresols from the thus separated monosulto acids, all substantially as described.

11. That improvement in the production of meta-cresol which comprises employing a mixture rich in meta-eresol and a limited quantity of sulfuric acid, and crystallizing out of the said mixture the component which retains the meta-eresol.

In witness whereof I have hereunto set. my hand in the. presence of two subscribing witnesses.

FRANZ ELGER. \Yitnesses HEINRICH KUBLI, PETER Miz'rzonu. 

